Unit Converter
HbA1c
HbA1c Calculator: NGSP ↔ IFCC Conversion & Estimated Average Glucose (eAG)
What Is HbA1c?
HbA1c (glycated hemoglobin) reflects the average blood glucose exposure over the previous 2–3 months. It measures the proportion of hemoglobin molecules that have glucose attached, making it a cornerstone test for diagnosing and monitoring diabetes.
Unlike fasting or post-meal glucose tests, HbA1c is not influenced by short-term fluctuations, illness, or daily meals.
Global Standardization of HbA1c Reporting
To ensure consistency and comparability of HbA1c results worldwide, international diabetes and laboratory organizations recommend standardization using the reference measurement system developed by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC).
Under this system:
- HbA1c is reported in mmol/mol, the official SI unit
- Values differ numerically from the traditional percentage (%) system
- Direct comparison requires a validated conversion equation
At the same time, many clinicians and patients—especially in India and the USA—are familiar with HbA1c expressed as a percentage (%), standardized through the National Glycohemoglobin Standardization Program (NGSP), which is aligned with the DCCT trial.
✅ International Recommendation
Major diabetes organizations in the US and Europe recommend dual reporting of HbA1c:
- mmol/mol (IFCC, SI unit) for scientific accuracy
- % (NGSP) for clinical familiarity and patient understanding
This approach improves communication, reduces errors, and supports safe clinical decision-making across countries and laboratories.
❌ HbA1c Is NOT Reported in mg/dL or mmol/L
A critical and often misunderstood point:
HbA1c is NOT a glucose concentration.
- mg/dL and mmol/L are concentration units used for plasma glucose
- HbA1c represents a ratio of glycated hemoglobin to total hemoglobin
Therefore:
- ❌ mg/dL → invalid for HbA1c
- ❌ mmol/L → invalid for HbA1c
- ✅ % → valid
- ✅ mmol/mol → valid
If HbA1c is reported in mg/dL or mmol/L, it is incorrect reporting.
Accepted Units for HbA1c
1. NGSP / DCCT-Aligned System
- Unit: % (percentage)
- Reported as HbA1c %
- Commonly used in India, USA, and many clinical laboratories
- Diabetes diagnostic cutoff: 6.5%
2. IFCC System (SI Standard)
- Unit: mmol/mol
- Expressed as mmol of glycated Hb per mol of total Hb
- Used in Europe, UK, Australia, and scientific publications
- Diabetes diagnostic cutoff: 48 mmol/mol
Standard HbA1c Conversion Formula (NGSP ↔ IFCC)
From % to mmol/mol
HbA1c (mmol/mol) = (HbA1c % − 2.15) × 10.929
From mmol/mol to %
HbA1c (%) = (HbA1c mmol/mol × 0.09148) + 2.15
These equations are the official IFCC–NGSP master equations and are used worldwide.
Common HbA1c Equivalents
| HbA1c (%) | HbA1c (mmol/mol) |
|---|---|
| 5.0 | 31 |
| 5.7 | 39 |
| 6.0 | 42 |
| 6.5 | 48 |
| 7.0 | 53 |
| 8.0 | 64 |
| 9.0 | 75 |
| 10.0 | 86 |
Clinical Interpretation of HbA1c
| Category | HbA1c (%) | HbA1c (mmol/mol) |
|---|---|---|
| Normal | < 5.7 | < 39 |
| Prediabetes | 5.7 – 6.4 | 39 – 47 |
| Diabetes | ≥ 6.5 | ≥ 48 |
These thresholds align with recommendations from the American Diabetes Association, WHO, and IFCC.
Estimated Average Glucose (eAG)
Estimated Average Glucose (eAG) translates HbA1c into an average glucose value that patients recognize from daily glucose monitoring.
- eAG is not HbA1c
- eAG is expressed in mg/dL or mmol/L
- It is calculated from HbA1c, not measured directly
This calculator automatically estimates:
- eAG (mg/dL)
- eAG (mmol/L)
based on internationally accepted equations.
About This HbA1c Calculator
This HbA1c calculator is designed to support international reporting standards and everyday clinical use. It allows:
- Instant conversion between HbA1c % (NGSP) and mmol/mol (IFCC)
- Automatic calculation of estimated average glucose (eAG)
- Conversion of glucose values between mg/dL and mmol/L
- Real-time updates entering any value updates all related fields instantly
The formulas used are globally validated and suitable for:
- People with diabetes
- Doctors and diabetes educators
- Clinical laboratories
- Medical students and researchers
Key Clinical Pearl
HbA1c has only two valid units: % and mmol/mol.
If you ever see HbA1c reported in mg/dL or mmol/L, it is incorrect.
References
- IFCC Working Group on HbA1c Standardization
- NGSP (National Glycohemoglobin Standardization Program)
- Tietz Textbook of Clinical Chemistry, 8th Edition
- ADA Standards of Medical Care in Diabetes